This chapter overviews the diagnostic strategy for endometriosis, encompassing clinical symptoms, examination, imaging techniques, and biological markers. Within the realm of imaging techniques, particular attention is devoted to discussing the diagnostic efficacy of transvaginal ultrasonography (TVUS) and magnetic resonance imaging (MRI). Each modality’s strengths and limitations are thoroughly analyzed, elucidating the nuanced advantages and inconveniences associated with their use in diagnosing endometriosis. Notably, MRI emerges as a notably sensitive tool, capable of discerning subtle pathological changes indicative of endometriosis, whereas TVUS exhibits commendable specificity in delineating anatomical details. The integration of these imaging modalities with clinical assessment holds promise for enhancing diagnostic accuracy. Moreover, the article delves into the decision-making algorithms devised by prominent French and European medical societies, shedding light on the structured approaches employed by healthcare professionals in diagnosing endometriosis. Additionally, it offers specialized insights into tailoring diagnostic strategies to address the unique needs and challenges encountered in adolescent patients. Finally, this article provides a nuanced understanding of the diagnostic intricacies inherent in managing endometriosis across diverse patient populations.